In Happy Feet, an emperor penguin named Mumble embarks on an epic quest to find out what's causing his colony's food—fish—to dwindle.

The culprit, not surprisingly, turns out to be humans.

It's a story that mirrors real life. From Antarctica to the Galápagos Islands, penguins find themselves increasingly threatened by human activity. Threats include overfishing, oil spills, human encroachment, and global warming.

Gary Miller is a behavioral ecologist who worked as a penguin consultant to the Happy Feet filmmakers.

"Penguin populations all over the world are being affected by things like global warming and by food reduction in areas where they breed," Miller said in a telephone interview from Perth, Australia, where he is affiliated with the University of Western Australia.

Penguins live exclusively in the Southern Hemisphere and are found as far north as Ecuador's Galápagos Islands (Ecuador map and facts).

The emperor penguin is the largest penguin species and also one of the few found in Antarctica. It stands about 4 feet (122 centimeters) tall and weighs up to 90 pounds (41 kilograms).

The emperor penguins' breeding ritual during the harsh Antarctic winter months was depicted in the documentary March of the Penguins and plays an important role in the story of Happy Feet. (National Geographic Feature Films co-distributed March of the Penguins and is part of the National Geographic Society, as is National Geographic News.)